Protease inhibitors (PIs), a type of anti-HIV drug, are known to cause increased lipids (fats) in the blood of HIV-infected patients. EFV also is known to increase blood fats. HIV-infected patients who take PIs and/or EFV may need to take fat-lowering drugs to correct this problem. So it is important to look at possible drug interactions when these drugs are taken together. This study will see if taking EFV or NFV, a protease inhibitor, affects the blood level of simvastatin, atorvastatin, or pravastatin (all fat-lowering drugs). To obtain results more quickly, the study population will be healthy HIV-negative volunteers.